Spontaneous Reduction in Mitral Valve Regurgitation in Three Dogs With Severe Myxomatous Mitral Valve Disease: An Unusual Case Report

Background Myxomatous mitral valve disease (MMVD), the most common heart disease in small‐breed dogs, is characterized by mitral regurgitation (MR) resulting from valvular degeneration, which may progress to left‐sided heart failure. This report describes the cases of three dogs with severe MMVD (American College of Veterinary Internal Medicine Stages C or D) who exhibited an unexpected spontaneous reduction in MR despite continued valve degeneration. Case Presentation Three dogs initially presented with symptoms of heart failure and left atrial and ventricular enlargement. Standard treatment, including diuretics, improved their conditions; however, further monitoring revealed that the coaptation gap decreased due to mitral valve thickening, leading to a reduction in MR. This was accompanied by a significant decrease in heart size. As a result, diuretics were discontinued, and all dogs were successfully managed with pimobendan alone. Conclusions To our knowledge, this is the first report of spontaneous MR reduction in MMVD, where coaptation gap narrowing played a role in clinical improvement. These cases may broaden the current understanding of MMVD progression, suggesting that, in rare instances, changes in cardiac remodelling and clinical status can occur. Further research is warranted to better understand the underlying mechanisms.